Several systems have been developed for inspecting the electrical leads of various semiconductor devices or so called "packages". Systems have been developed which measure the positional integrity of semiconductor devices which have straight or bent prong type leads extending from one or more sides of a rectangular device package and systems and methods have been developed for determining the positional integrity and coplanarity of semiconductor devices which include plural, so-called solder ball type leads arranged in an array on a surface of the device. The measurement of the coplanarity of the lead ends of prong type leads and, particularly, the coplanarity of solder ball or ball grid array devices is important in order to assure the integrity of an electrical circuit using these devices upon assembly of the devices to the circuit.
For example, systems have been developed which use back lighting of the semiconductor package and view the package with a charge coupled device or so-called CCD camera to capture an image of the leads. If leads extend from more than one side of the package or device, the device is rotated two or more times to capture an image of the other sets of leads and these images are compared to a template to determine if the leads are in a correct position. The imaging and comparison process may be carried out on a digital microprocessor or so-called central processing unit (CPU) to increase the speed and efficiency of the inspection process. This type of system can be used to take the three dimensional height measurement of semiconductor devices with so-called "gull wing" shaped prong type leads but is not suitable for measuring or inspecting devices with so called solder ball or similar type leads.
Systems have also been developed which use a combination of lasers, triangulation and a CCD camera to obtain two dimensional and three dimensional measurements of prong type leads or solder ball type leads. Typically, the semiconductor devices being measured reside in a tray or other holding structure while a laser head scans one or more leads at the same time. U.S. Provisional patent application 60/051,239 filed Jun. 30, 1997 and U.S. patent application Ser. No. 08/890,814 filed Jul. 11, 1997, both assigned to the assignee of the present invention, describe apparatus for two dimensional and three dimensional inspection of semiconductor device leads.
Still further, systems have been developed which project light from multiple sources to form shadows of the semiconductor device leads and, by measuring the length of the shadows, the three dimensional "height" information of the leads can be obtained.
Known methods and apparatus for making semiconductor device lead measurements or inspections have not been adapted for performing the inspection measurements for both two dimensional (2D) and three dimensional (3D) measurements combined, or while the device is moving from one position to another. Known apparatus also require complicated mechanisms to manipulate the devices during the inspection process and require that the device be held stationary while the inspection process is performed. Moreover, known lead inspection systems and methods have not been readily adaptable to measuring semiconductor devices or packages with both the gull wing or similarly configured prong type leads and solder ball type leads in an arrangement which requires little or no modification of the system or method during the lead inspection process.
In particular, it has been noted that known systems which rely on a combination of lasers and triangulation to obtain the three dimensional height or coplanarity measurement of a lead array can be particularly sensitive to the reflectivity of the lead material, which may vary considerably depending on the material used for the leads, the degree of oxidation of the lead material or other conditions which might affect the reflectivity of the lead surface.
Accordingly, there has been a continuing need to develop an inspection system and method for inspecting the electrical leads of semiconductor packages of both the prong type as well as the solder ball type without requiring substantial modification to the system when measuring one type versus the other while making measurements with accuracy, regardless of the reflectivity characteristics of the lead material. Moreover, there has also been a need to develop a system and method which is capable of measuring the leads of semiconductor devices more efficiently and expeditiously, particularly considering the massive quantities of such devices that are manufactured at substantial production rates. In this latter regard there has been a need to develop an inspection system and method which may be interposed in a production process at some stage between the finished fabrication of the semiconductor device and its application to an electrical circuit. It is to these ends that the present invention has been developed.